1) Field of the Invention
This invention relates to an automatic delay equalizer and an automatic delay equalization method as well as an automatic delay and amplitude equalizer and an automatic delay and amplitude equalization method suitable for use to automatically compensate for a delay characteristic (delay distortion) and/or an amplitude characteristic (amplitude distortion) which appear in a communication signal (input signal) from a delay frequency characteristic and/or an amplitude frequency characteristic of a transmission line.
2) Description of the Related Art
It is known that, not only transmission lines for radio communication such as digital multiplex microwave communication, but all transmission lines (including the space) have two different types of linear characteristics of an amplitude frequency characteristic and a delay frequency characteristic, and the characteristic of a transmission line is influenced by the two characteristics.
For example, if the two characteristics are flat with respect to the frequency, then it is basically possible to decode (demodulate) a transmission signal (modulation signal) itself from a reception signal (input signal), but if they are not flat, then a xe2x80x9cdistortion (linear distortion)xe2x80x9d is produced in the demodulation signal and degrades the demodulation characteristic.
In order to equalize and compensate for such a linear distortion as described above, various amplitude equalizers and delay equalizers have been proposed wherein the amount (characteristic) of the linear distortion produced by a characteristic of a transmission line is measured in advance and equalization (compensation) of the reception signal is performed on the assumption that the distortion amount measured does not exhibit a variation (in other words, on the assumption that the linear distortion is a distortion of a fixed amount).
However, an actual transmission line suffers also from a distortion which varies dynamically as fading such as a distortion which is produced in a space transmission line or a distortion which is fluctuated by a variation of the cable length which is caused by a temperature variation or some other variable such as a distortion which is produced in aware transmission line. Therefore, it is a matter of course that the linear distortion described above is not a distortion of a fixed amount. Accordingly, an amplitude equalizer or a delay equalizer which performs equalization on the assumption that the linear distortion is a distortion of a fixed amount cannot sufficiently compensate for the linear distortion.
As regards an amplitude distortion which depends upon, an amplitude frequency characteristic, a technique has been proposed, for example, in Japanese Patent Laid-Open Application No. Heisei 8-163005 wherein the fluctuating distortion amount can be detected on the real time basis so that even the fluctuating distortion can be automatically equalized and compensated for. However, as regards a delay distortion which depends upon a delay frequency characteristic, neither means for detecting the amount of a distortion which currently influences on a reception signal nor means for automatically equalizing the thus detected distortion has been realized as yet.
It is an object of the present invention to provide an automatic delay equalizer and an automatic delay equalization method which can detect a delay characteristic of an input signal and automatically compensate for the delay characteristic.
It is another object of the present invention to provide an automatic delay and amplitude equalizer and an automatic delay and amplitude equalization method which can detect a delay characteristic and an amplitude characteristic of an input signal and automatically compensate for both of the characteristics.
In order to attain the objects described above, according to an aspect of the present invention, there is provided an automatic delay equalizer for compensating for a delay characteristic of an input signal, comprising an inclination delay equalization section for compensating for the delay characteristic of the input signal in accordance with an inclination delay characteristic, and a control section for discriminating a direction of variation of a value of a first one of a pair of digital demodulated signals of the input signal, detecting error information from a second one of the digital demodulated signals which is orthogonal to the first signal and outputting a control signal for the inclination delay equalization section based on a correlation between the error information and the direction of variation of the value of the first signal.
According to another aspect of the present invention, there is provided an automatic delay equalization method, comprising a detection step of detecting inclination information of a delay characteristic of an input signal, and a compensation step of compensating for the delay characteristic of the input signal based on the inclination information of the delay characteristic of the input signal detected by the detection step.
With the automatic delay equalizer and the automatic delay equalization method, since the inclination information of the delay characteristic of the input signal is detected and the delay characteristic of the input signal is compensated for based on the inclination information of the delay characteristic, the fluctuating delay distortion amount can be detected on the real time basis and the distortion can be equalized and compensated for automatically. Consequently, the accuracy in signal demodulation can be improved significantly.
According to a further aspect of the present invention, there is provided an automatic delay equalizer for compensating for a delay characteristic of an input signal, comprising an inclination delay equalization section for compensating for the delay characteristic of the input signal in accordance with an inclination delay characteristic, and a control section for discriminating a direction of variation of a value of a first one of a pair of digital demodulated-signals of the input signal, detecting error information from a second one of the digital demodulated signals which is orthogonal to the first signal and producing a first correlation signal based on a correlation between the error information and the direction of variation of the value of the first signal, for discriminating a direction of variation of a value of the second signal, detecting error information from the first one of the digital demodulated signals which is orthogonal to the second signal and producing a second correlation signal based on a correlation between the error information and the direction of variation of the value of the second signal and for producing a control signal for the inclination delay equalization section based on the first correlation signal and the second correlation signal and outputting the control signal.
With the automatic delay equalizer, since the direction of variation of the value of a signal and the error information are detected for both of the digital demodulated signals and the control signal for the delay characteristic compensation is produced based on the correlations between them, the detection sensitivity and the accuracy of the control signal can be improved significantly when compared with the automatic delay equalizer according to the first-described aspect of the present invention described above. Consequently, the accuracy of the automatic delay equalizer can be improved further significantly.
According to a still further aspect of the present invention, there is provided an automatic delay and amplitude equalizer for compensating for a delay characteristic and an amplitude characteristic of an input signal, comprising an inclination delay equalization section for compensating for the delay characteristic of the input signal in accordance with an inclination delay characteristic, an inclination amplitude equalization section for compensating for the amplitude characteristic of the input signal in accordance with an inclination amplitude characteristic, and a control section for discriminating a direction of variation of a value of a first one of a pair of digital demodulated signals of the input signal, detecting error information from a second one of the digital demodulated signals which is orthogonal to the first signal and outputting a control signal for the inclination delay equalization section and another control signal for the inclination amplitude equalization section based on a correlation between the error information and the direction of variation of the value of the first signal.
According to a yet further aspect of the present invention, there is provided an automatic delay and amplitude equalization method, comprising a detection step of detecting inclination information of a linear distortion characteristic of an input signal, and a compensation step of compensating for a delay characteristic and an amplitude characteristic of the input signal based on the inclination information of the linear distortion characteristic of the input signal detected by the detection step.
With the automatic delay and amplitude equalizer and the automatic delay and amplitude equalization method, since the inclination information of the linear distortion characteristic of the input signal is detected and the delay characteristic and the amplitude characteristic of the input signal are compensated for based on the inclination information of the linear distortion characteristic, not only the delay distortion but also the amplitude distortion can be detected on the real time basis and the distortions can be equalized and compensated for automatically. Consequently, the accuracy in signal demodulation can be improved further significantly.